This proposal is designed as a molecular approach to persistent virus infection, using coronaviruses as the experimental system. Coronaviruses have been selected because (1) murine coronaviruses cause persistent infection and chronic progressive neurological disease in rodents; (2) human coronaviruses are widespread in the human population; and (3) persistent infection of cell cultures are readily initiated and provide a model for study at the molecular level. Molecular Studies. One major goal of this proposal is to characterize the subgenomic putative messenger RNAs (mRNAs) of the mammalian coronaviruses, mouse hepatitis virus and human coronavirus 229E. Complementary DNA (cDNA) will be synthesized using positive stranded genome RA as template. This cDNA will then be used to determine the size, number, cellular location, kinetics of accumulation, and mechanism of genesis of the virus-specific subgenomic RNAs, synthesized during acute infection of cell cultures. Molecular hybridization will also be used to determine the homology between the genome RNAs of the murine and human viruses. Genome RNA and virus-specific RNAs from infected cells will be translated in cell-free systems, to elucidate the translation scheme of coronavirus proteins and to begin to map the genome. Biological Studies. The second major goal of this proposal is to use the information described above, to start to explore some of the biological properties of coronaviruses. (a) Persistent coronavirus infections in cell culture will be investigated with respect to changes in viral genome or in viral mRNAs. Defective interfering particles, if found, will be characterized both biochemically and with regard to biological activity. (b) An attempt will be made to characterize virion and mRNAs associated with persistent CNS infection of rodents.